1. Field of the Invention
The present invention relates to an image forming optical system and an image pickup apparatus including the system.
2. Description of the Related Art
In the recently prevalent image pickup apparatus such as a compact digital camera or a cellular phone equipped with a camera, there is used an electronic image sensor such as a CCD image sensor or a CMOS type image sensor.
Such an electronic image sensor has a characteristic that adequate color cannot be reproduced, when the incidence angle of ray upon the image sensor is large.
Therefore, in an image forming optical system for use in the above image pickup apparatus, the exit pupil is positioned far from the image pickup surface of the electronic image sensor to thereby reduce the incidence angle of ray to be incident on the image sensor.
As such an image forming optical system for use in the image pickup apparatus, there are known image forming optical systems described in, for example, the following documents (1) to (9):
(1) Japanese Patent Application Laid-Open No. 2005-24969;
(2) Japanese Patent Application Laid-Open No. 2003-140039;
(3) Japanese Patent Application Laid-Open No. 2001-56434;
(4) Japanese Patent Application Laid-Open No. 2001-21800;
(5) Japanese Patent Application Laid-Open No. 2000-105334;
(6) Japanese Patent Application Laid-Open No. 10-293246;
(7) Japanese Patent Application Laid-Open No. 09-297264;
(8) Japanese Patent Application Laid-Open No. 09-189856; and
(9) Japanese Patent Application Laid-Open No. 09-166748.